The present invention relates to an electron beam integrated circuit tester. More particularly, the present invention relates to an electron beam integrated circuit tester in which the position of a secondary beam at the input of a spectrometer is independent of the primary scanning so that defocusing of the spectrometer is avoided.
For testing integrated circuits, the use of test apparatus derived from electronic scanning microscopes is known. Generally, in these apparatuses, a primary electron beam is finely focused on each point of the integrated circuit to be tested and the electric potential thereof is determined by measuring in a region at a certain potential the energy of the secondary electrodes which are generated by bombardment of the primary beam. Examples of testers operating on this principle are described in the articles entitled:
Electron Beam Testing of VLSI circuits" by Eckard Wolgang et al and published in the IEEE Journal of solid state circuits, vol. sc 14, no. 2, April 1979, and
"Fundamentals of electron beam testing of integrated circuits" by E Menzel and E. Kubalek and published in the review Scanning, vol. 5, 103.122 (1983).
In these testers, the space between the circuit to be tested and the pole piece belonging to the last focusing lens and facing it is occupied by the secondary electron spectrometer.
The qualities of a spectrometer, luminosity and resolution power, are all greater for greater dimensions. But, on the other hand, the qualities of the lens are weaker (higher abberations) the greater its focal distance. So in the design of the testers of known type a compromise is sought between the dimensions of the spectrometer and the focal distance of the last lens. Furthermore, placing the spectrometer between the lens and integrated circuit becomes troublesome if it is desired to place also in this gap accessory devices such as power supply prods for testing integrated circuits on a wafer before cutting up of the wafer.
The present aim of the invention is to overcome the above drawbacks.